The present invention relates to isolation and use of genes important in plant nutrition. In particular, it relates to polynucleotides encoding high affinity potassium uptake transporters, recombinant constructs comprising the polynucleotides, and transgenic organisms comprising the polynucleotides.
Potassium (K+) is the most abundant cation in higher plants and plays vital roles for plant nutrition, growth, tropisms, enzyme homeostasis and osmoregulation. Epstein et al., Proc. Natl. Acad. Sci. USA 49:684-692 (1963); Kochian et al., Adv. Botany Res. 15:93-177 (1988); and Schroeder et al., Annu. Rev. Biophys. Biomol. Struct. 23:441-471 (1994). Potassium accumulation can be rate-limiting for agricultural production. K.sup.+ -uptake from soils into roots is largely mediated by high-affinity K.sup.+ -uptake (K.sub.m .apprxeq.10-40 .mu.M). Newman et al. Plant Physiol. 84:1177-1184 (1987); Fernando et al., Plant Physiol. 100:1269-1276 (1992); and Maathuis et al. Planta 191:302-307 (1993). While potassium channels allow low-affinity potassium-uptake (Schroeder et al., Proc. Natl. Acad. Sci. USA 84:4108-4112 (1987); Schroeder et al., Proc. Natl. Acad. Sci. USA 88:11583-11587 (1991)), the prior art has yet to elucidate the transport mechanism and structure of the high-affinity potassium nutrition pathway.
High salt levels in soils and the ensuing sodium (Na+) influx into plants severely reduce agricultural production, with .apprxeq.30% of irrigated soils being affected by high salt concentrations worldwide. Greenway et al., Annu. Rev. Plant Physiol. 31:149-190 (1980). The molecular mechanisms of Na+-uptake into plants remain unknown. It is known, however, that K.sup.+ strongly competes with both Na.sup.+ -and Cs.sup.+ -uptake and Cs.sup.+ toxicity in plant root. Rains et al., Science 148:1611 (1965); Welch et al., Proc. Natl. Acad. Sci. USA 61:447-453 (1968); and Sheehan et al., Plant J. 3:647-656 (1993). Thus, information about potassium transporters may be useful in developing plant varieties tolerant of environmental stresses associated with alkali metal toxicities.
Because of its importance to plant nutrition, the isolation and characterization of genes encoding plant proteins involved in potassium uptake would be extremely useful in the engineering of various crop plants. In addition, expression of such genes could be modified as necessary to provide other advantages, such as salt tolerance. The present invention addresses these and other needs.